Topic 13

The Somatic Sensory System

Lange

Biology 463 - Neurobiology

Introduction

Somatic Sensation– Enables body to feel, ache, chill– Responsible for touch and pain– Somatic sensory system: Different from other systems

• Receptors: Broadly distributed• Responds to many kinds of stimuli

Touch

• Types and layers of skin– Hairy and glabrous (hairless - e.g., palms)– Epidermis (outer) and dermis (inner)

• Functions of skin– Protective – Prevents evaporation of body fluids– Provides direct contact with world

• Mechanoreceptors– Most somatosensory receptors are mechanoreceptors

Touch

• Mechanoreceptors • Pacinian corpuscles• Ruffini's endings• Meissner's corpuscles• Merkel's disks• Krause end bulbs

Touch

Mechanoreceptors – Small and large receptive fields

Touch

Mechanoreceptors – Two-point

discrimination• Receptive field

density• Receptive field

size

Touch

Primary Afferent Axons– AC– C fibers mediate pain and temperature– Amediates touch sensations

Pain Perception

Primary Afferents and Spinal mechanisms– First pain and second pain– Referred pain: Angina

Touch

The Spinal cord– Spinal segments (30)- spinal nerves within 4 divisions of spinal

cord

Touch

The Spinal cord– Dermatomes- 1-to-1 correspondence with segments– Shingles

Touch

Dorsal Column–Medial Lemniscal Pathway

– Touch and proprioception

Touch

Homuncular Mapping

Touch

Homuncular Mapping of a variety of mammals shows differences in distribution of sensory structures that relate to habitat and environmental success.

Temperature

Thermoreceptors– Hot and cold receptors

END.